Different crystal chemistries of the Cd-117 - In-117 and Cd-111m - Cd-111 probes in LiNbO3 and LiTaO3 studied by the time-differential perturbed-angular-correlation technique

摘要

The nuclear-electric-quadrupole interactions at In-117 and Cd-111 nuclei arising from Cd-117 and Cd-111m, respectively, each chemically introduced in ferroelectric LiNbO3 (T-C = 1483 K) and LiTaO3 (T-C = 938 K) poly crystals, were studied by measuring the time-differential perturbed angular correlation of gamma rays over a temperature range from 4.2 to 1243 K. Well-defined, essentially single, static electric quadrupole frequencies were observed for In-117 and Cd-111 in the oxides. It has been established that both In and Cd occupy the Li sites of LiNbO3 and LiTaO3. In the case of LiTaO3, the temperature dependences of the quadrupole frequencies omega(Q) of In-117 and Cd-111 clearly change at around T-C = 938 K, reflecting the ferroelectric-to-paraelectric phase transition. In both oxides, it might be expected that the temperature dependence of omega(Q) of In-117 would agree with that of Cd-111. However, it is so only at low temperatures, including room temperature. There is a significant difference at high temperatures: omega(Q) of In-117 is strongly dependent on temperature, whereas omega(Q) of Cd-111 is weakly dependent. It is considered that the Cd ions at the Li sites are in peculiar physicochemical states. [S0163-1829(99)12841-8]. [References: 28]